The invention disclosed in Japanese Unexamined Patent Application Publication No. 2008-168440 relates to a bookbinding system in which an image forming apparatus is connected to a bookbinding device that carries out a bookbinding operation including a cutting process. The bookbinding system includes: a size obtaining unit (S101) that obtains the size of a completed bound book; an allowable range obtaining unit (S103) that obtains the allowable range of a cutting width in which a cutting process can be performed on the basis of the obtained size of the completed bound book; and paper sheet selection devices (S104 and S105) that determine the size of paper sheets that can be cut on the basis of the size of the completed bound book and the allowable range obtained by the aforementioned units to select a paper feeding tray. According to the bookbinding system, printing and bookbinding can be executed while selecting paper sheets with an appropriate size in accordance with the size of the paper sheets of the completed bound book.